The best open source alternative to InVision is Presentator.io, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 50 alternatives to InVision and seven of them is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to InVision are Wireflow (Free, Open Source), quickMockup (Free, Open Source), mydraft.cc (Free, Open Source) and Quant-UX (Free, Open Source).
Online tool for creating mockups in the browser. Use your browser’s save function to save the file (just html for view only, complete save for an editable version) or export to codepen for others to view.